This invention relates to borate phosphors and methods of making borate phosphors. In particular, this invention relates to flux materials for making yttrium gadolinium borate phosphors.
The phosphor hosts YBO3 and GdBO3 have been known for a long time. For example, Avella et al. described in 1967 the luminescence of these materials activated with terbium or europium under cathode ray excitation. J. Electrochem. Soc. 114 (1967) 613. Yet, until recently, these materials have seen little commercial use because less expensive and/or more efficient phosphors were available for general lighting and cathode ray applications.
With the advent of plasma display panel (PDP) technology, there has been a renewed interest in these phosphors, especially the red-emitting europium-activated phosphors. The reason for the renewed interest derives from the ability of these materials to convert xenon plasma radiation (about 147 nm to about 172 nm) into visible light better than most other PDP phosphor candidates. In fact, europium-activated solid solutions of YBO3 and GdBO3 are the phosphors of choice for PDP flat panel display technology.
The conventional method of synthesis for these materials as described by Avella et al. is less than desirable for PDP applications. The phosphor produced by the conventional method is highly agglomerated which makes it difficult for PDP panel manufacturers to apply smooth, uniform phosphor coatings. Furthermore, conventional deaggomeration methods such as milling are undesirable since they tend to reduce the brightness of the phosphor. Thus, it would be an advantage to provide a phosphor having a discrete particle morphology which does not require deagglomeration.
It is an object of the invention to obviate the disadvantages of the prior art.
It is another object of the invention to provide a method of making a borate phosphor having a discrete particle morphology without deagglomeration.
In accordance with one object the invention, there is provided a method of making a borate phosphor having a discrete particle morphology. The phosphor has the general formula:
(Y1xe2x88x92xxe2x88x92y,Gdx,Acy)BO3 
where Ac is a trivalent rare earth element;
x is from 0 to 1xe2x88x92y;
y is from greater than 0 to about 0.2;
The method comprises forming a mixture of yttrium oxide, gadolinium oxide, an oxide of the rare earth element, boric acid and a flux, the flux comprising a salt of barium, sodium, potassium, or a combination thereof; and firing the mixture at a temperature and for a time sufficient to form the phosphor.